Greek police say they have made their biggest breakthrough yet in the fight against the left-wing guerrilla group November 17.

There is still work to be done to dismantle the network

Prime Minister Costas Simitis

The fingerprints of a man held in custody have been connected with a murder blamed on the organisation, police say.

It is the first time the Greek authorities have struck a blow against the group which has been linked to the murders of high-profile politicians, defence officials and diplomats. during its 27 years' existence.

The detained man, Savas Xiros, has been under police guard in hospital since Saturday night, when he was injured after a bomb he had been carrying exploded.

Police alleged he had been attempting to blow up the ticketing office of a shipping company in Piraeus harbour.

Clues

Mr Xiros is alleged to have been involved in the killing of Greek businessman Costas Peratikos in 1997.

Police raided a flat in central Athens

Police say his fingerprints match those found on a car used by November 17 during the killing.

On Wednesday night the authorities launched a highly publicised raid on a flat in Athens which Mr Xiros had been renting.

They found a substantial arms cache allegedly belonging to the group and including mortars, rifles and grenades.

Greek Prime Minister Costas Simitis said the suspect's arrest and the discovery of the weapons were "significant steps" in the fight against terrorism.

But, he conceded, "there is still work to be done to dismantle the network".

Greece - which is hosting the 2004 Olympics - has been under pressure to crack down on November 17 in the run-up to games.

Elusive

The secretive group is on the US State Department's terrorism list.

Xiros's fingerprints allegedly link him to a 1997 murder

In its annual report to Congress last year, the State Department said Greece's failure to arrest members of the organisation was "troubling".

November 17 takes its name from the date of a 1973 student uprising, which was crushed by the army.

Its first known attack came in December 1975, when the head of the US Central Intelligence Agency in Athens, Richard Welch, was shot dead.

The group has admitted responsibility for 21 killings, including those of four US diplomats.

Its most recent victim was British defence attache Stephen Saunders - who was killed two years ago.